The oSPIM is an excellent platform for light sheet imaging
of samples in standard culture dishes. The light sheet is
generated using the inverted microscope and imaged from
above using a tilted water dipping objective with NA as
high as 1. 1 (<300 nm transverse resolution). The inverted
microscope is also available for conventional imaging
modalities (e.g. confocal, wide feld, or TIRF)

the 30 W Spectra-Physics Spirit laser) is
first frequency-doubled to 520 nm. A
small portion of the residual 1040 nm
light is focused into an appropriate me-
dium to generate a broad supercontinuum, which acts as a seed for the optical parametric amplification process.
Amplification is realized in two consec-
utive stages: the non-collinear scheme
used in the first stage generates a large
spectral bandwidth that can subsequently be temporally recompressed to short
pulses. The second, or collinear, stage
gives access to both signal and idler
wavelengths, and thus a broadly tunable output. Both stages are pumped
with the high-power 520 nm beam.
The signal and idler beam are spec-
trally broad and temporally dispersed.
Both output beams are finally recom-
pressed, the signal in a prism-based
scheme and the idler in a bulk scheme, to
achieve extremely short pulse durations
(<100 fs) and ultra-high peak power

(> 20 MW). In particular, the idler covers the

1200–2500 nm spectral range with peak
powers of more than 20 MW, a value
that exceeds the peak-power threshold
for three-photon imaging.

Reaching thehippocampus in vivo

Chris Xu and his collaborators at Cornell
are pioneers in the development of 3PM
and its use for functional imaging deep
in the brain. In a recent study, Xu’s team
demonstrated the optical recording of
spontaneous activity from neurons in
the hippocampus down to 1 mm within an intact mouse brain. 4 “We are now
able to see neurons in action in an intact
mouse brain at single-cell resolution and
at depths that were not previously possible, which opens new opportunities for
neuroscience research,” he says.

The work (see frontis, page 31) wasdone using a custom-built three-photonmicroscope and a non-collinear opticalparametric amplifier (Spirit-NOPA)pumped by a single-box automated